1. Field of the Invention
The present invention relates to a vehicle surroundings monitoring device mounted on a vehicle and used for monitoring of surroundings around the vehicle and, more particularly, to a vehicle surroundings monitoring device for alarming a driver to enable the driver to avoid contact with or collision against an obstacle particularly at the time of lane change or the like.
The entire content of the basic Japanese Patent Application from which the priority under the Convention is claimed in this application is hereby incorporated by reference into this application.
2. Description of the Related Art
Various radar devices have been proposed which are widely used as a vehicle surroundings monitoring device, a controller for controlling the distance of a vehicle from another vehicle, etc., by being mounted on vehicles.
For example, Japanese Patent Application Laid-Open No. Sho 54-45040 discloses a vehicle surroundings monitoring device having a radar unit. This device is formed by using a portion of a fender mirror and a fender portion of a vehicle.
In the above-described conventional device, a mirror surface is used as an antenna reflector, and electric waves are externally radiated to the mirror surface by using a feeder horn antenna. The feeder horn is therefore exposed to the outside and there is a possibility breakage of the feeder horn or failure of maintenance of the desired performance due to external causes.
Therefore, it is desirable that such an antenna should be housed in a body of a mirror assembly. However, if an antenna is incorporated in a mirror assembly, electric waves from the antenna are reflected by the mirror to cause the radar to operate as if an obstacle always exists within a short distance from the vehicle. When an object actually exists within a short distance from the vehicle, the radar cannot detect the object if the distance resolution of the radar is not sufficiently high. Also, the distance measuring performance may be influenced by the reflection by the mirror to such an extent that the possibility of detection failure or a false alarm is high.
In view of the above-described problem, an object of the present invention is to provide a vehicle surroundings monitoring device in which reflection by a mirror is reduced to ensure the desired performance of distance measurement even in a short-distance range.
To achieve the above-described objects, according to one aspect of the present invention, there is provided a vehicle surroundings monitoring device which monitors surroundings around a vehicle, the device is characterized by comprising a transmitting antenna mounted in a door mirror assembly of the vehicle, said transmitting antenna for radiating transmitted waves through a mirror surface of a door mirror in the door mirror assembly, a receiving antenna mounted in the door mirror assembly, the receiving antenna for receiving, through the mirror surface of the door mirror, reflected waves from an object existing in the surroundings of the vehicle, and electric wave transmission surfaces formed as portions of the door mirror surface corresponding to opening surfaces for said transmitting and receiving antennas to limit reflection by the door mirror surface and to enable transmission of electric waves through the door mirror surface.
Also, the electric wave transmission surfaces in the door mirror surface are formed by partially removing a reflective film formed on the mirror surface.
Also, the electric wave transmission surfaces in the door mirror surface are formed by partially cutting off the mirror surface.
Also, the electric wave transmission surfaces in the door mirror surface are formed by forming metal slits in portions of the door mirror surface or through the entire door mirror surface.
In the vehicle surroundings monitoring device of the present invention, electric wave transmission surfaces for limiting reflection and for enabling transmission of electric waves are formed as portions of the door mirror surface corresponding to opening surfaces for the transmitting and receiving antennas, thereby limiting reflection by the door mirror surface and maintaining the desired short-range distance measuring performance to provide unerring alarm information to a driver.